TS 1109 
.C85 
Copy 1 



DEPARTMENT OF COMMERCE 



Circular 



OF THE 



Bureau of Standards 

S. W. STRATTON, Dirbct.or 



No. 107 
THE TESTING OF PAPER 



FEBRUARY 12, 1921 




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PRICE, 10 CERTS 

Sold only brtb* Supartnlendenl ol Documents, Govtmnunt Printing OtDca 

Washington, D. C. 



WASHINGTOW 

oovERmiBifT PRiNxmo orncB 

1921 



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DEPARTMENT OF COMMERCE 



Circular 



OF THE 



L|.t>. 



Bureau of Standards 

S. W. STRATTON, Director 



No. 107 
THE TESTING OF PAPER 



FEBRUARY 12, 1921 




PRICE, 10 CENTS 

Sold only by the Superintendent of Documents, Goveroment Printing Office 

Washington, D. C. 



WASHINGTON 
GOVERNMENT PRINTING OFFICE 



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klSRA«Y OF CONQRESS 

RECEIVED 
SOOUMiNTS QlV'StON 



THE TESTING OF PAPER 



ABSTRACT 

This circular contains information relating to the methods of testing and the appa- 
ratus employed in the paper laboratories of the Bureau of Standards for the routine 
testing of paper. In the introduction a brief description of the raw materials used, 
the size and importance of the paper industrj-, and the general groups or classes of 
paper are given. The classification of paper is only of a general nature. The pur- 
pose of such tests and the development of methods of testing is touched upon, and 
suggestions are given as to the methods of developing specifications. 

The testing of paper is divided into three groups, and the methods are classed as 
physical, chemical, and microsco])ical. Under each group, the various standard 
methods are given in detail with photographs of apparatus employed. No attempt 
is made in this circular to interpret results of tests. It is brought out that changes of 
temperature and humidit)- affect the physical qualities of paper, and for this reason a 
constant-temperature and humidity room has been installed. It has not been possible 
to give the relation between humidity and temperature changes and the physical 
characteristics of paper, but it is hoped to have this information available later. The 
chemical testing of paper is concerned with the determination of the amount and kind 
of filler or loading materials used and the amount and kind of sizing in the paper, 
and the methods are given in some detail, both qualitative imd quantitative. It 
is desirable to know the kinds of fibrous materials out of which a sheet of paper is made 
and for this purpose certain stains are used to color the fibers on a microscopical slide. 
The procedure is given, and siiggestions are made as to the value of microphotographs. 
A short working bibliography is included, as well as regulations for tests and methods 
of sampling and submission of samples for test. 



CONTENTS p^g^ 

I . Introduction 4 

1 . Size of industry 5 

2 . Raw materials 5 

3. Definition and types of paper 6 

II . Quality of paper 7 

1 . Purpose of tests 7 

2 . Development of test methods 7 

3. Specifications 8 

(a) Formulation g 

(6) Nomenclature 9 

(c) Quality standards 9 

(d) Technical practice 9 

III. Physical testing 10 

1 . Weight 10 

2 . Thickness 13 

3 . Bursting strength 14 

4. Tensile strength 15 

5. Folding endurance 17- 

6. Tearing strength 18 

7. Absorption 20 

8. Transparency 22 

3 



4 Circular of the Bureau of Standards 

Page 
IV. Chemical testing 23 

1 . Loading material 23 

2. Sizing 25 

(a) Total resins ^ 25 

(6) Starch 27 

(c) Glue 27 

V. Microscopical testing 28 

1 . Procedure 28 

2 . Estimation 31 

3. Microphotography 32 

VI. Bibliography 32 

1 . Books 32 

2. Periodicals 32 

3. Government publications 35 

VII . Regulations regarding tests 35 

I- Fees 35 

2. Sampling 37 

I. INTRODUCTION 1 

The testing of paper by means of scientific methods has received 
an increasing amount of attention in the United States during the 
past ID years. This has been brought about largely by the increase 
in the number of technically trained men in the industry and the 
desire of placing empirical and practical tests upon a more accurate 
basis. 

The pturpose of this circular is to describe the methods of testing 
paper as used by the paper section of the Bureau of Standards and 
adopted as a result of testing a large number of samples of various 
kinds of paper during a period of years. These methods are those 
that are in common use in paper- testing laboratories and are given 
to fill a need expressed by laboratories and the general public. 
Proposed new methods and special tests are not included in this 
circular, but these will be published, separately as they are 
developed. 

The structure of paper is such that there is variation in some ot 
its characteristics, even in a single sheet. It is therefore obvious 
that precaution must be taken to sample a lot of paper in such a 
way as to obtain a test sample representative of the whole lot. 
It is also necessary to make a sufficient number of tests in each case, 
in order that an average result may be obtained. It is important 
to obtain this average by testing lo sheets of paper, rather than by 
making lo tests on a single sheet. 

1 This circular was prepared by F. A. Curtis, chief, paper section. Bureau of Standards, and contains 
information relating to the methods of testing and the apparatus employed in the paper laboratories of this 
Bureau for the routine testing of paper. 



The Testing of Paper 5 

1. SIZE OF INDUSTRY 

The production of paper in the United States has increased ap- 
proximately 55 per cent in the last 10 years, and there is now being 
manufactured annually, in the United States, approximately 
7,000,000 tons of paper of all kinds. The pulp and paper industry 
in 1 9 14 ranked sixth among the industries of the United States in 
regard to the amount of capital invested and in regard to the value 
of the product, and ranked fourth in regard to the value added by 
manufacture. It can thus be readily seen that the pulp and paper 
industry is an important one, and there is little doubt but that tech- 
nical development is essential for the future of the industry. 

2. RAW MATERIALS 

Paper can be made from most fibrous vegetable matter, but 
technical difficulties, cost of manufacture, and grade of paper 
produced preclude the use of many fibrous materials. Wood 
pulp, old rags, old papers, straw, and old rope are the substances 
generally in use in this country. Wood pulp is produced by four 
processes, one of Vv'hich, "ground wood" pulp, is mechanical, 
while the other three, "sulphite," "soda," and "sulphate," are 
largely chemical. There are a large number of commercial grades 
of rags and waste paper. All these materials are used in different 
classes of paper for different pxuposes, or in many cases mixtures 
are made to produce certain qualities in paper. In addition to 
the fibrous material entering into the manufacture of paper, 
certain noncellulose materials are necessary or desirable. The 
addition of rosin sizing to paper pulp, and its precipitation by 
alum, gives the finished paper certain difficultly definable ciualities. 
Clays and similar materials, when added, produce a more even or 
smooth surface to the paper which is necessary for some kinds of 
printing. 

Experiments have been made, some of them a hundred years 
ago, to produce paper from various kinds of grasses and fibrous 
material. An incomplete list is here given: Asparagus, bagging, 
bamboo, banana, beet root, blue grass, bran, broom com, cabbage 
stumps, coconut husks, cottonseed hulls, cotton stalks, com 
husks, palm, esparto, ferns, flax, grapevines, hay, hemp, leaves, 
moss, mulberry, nettles, peat, plantain, reeds, rice straw, rushes, 
sawdust, seaweed, thistles, tow, and many others. Some of 
these experiments have been successful on a laboratory scale, 
some have even produced paper in large enough quantity for 
printing, but only a fe-w have ever reached a commercial standing. 

A study of Table i brings out an interesting change in the 
proportions of various raw materials used at various periods. 



Circular of the Bureau of Standards 



TABLE 1. — Percentage Proportions of Constituent Materials Used in Paper Making, 

by Decades, Since 1880 



Materials 



Rags 

Straw 

Wood pulp 

Old papers 

Miscellaneous. 



Per cent 
30 
40 



14 
16 



Per cent 
14 

21.5 
38 
21 
5.5 



Per cent 

8 

6.5 
61 
21 

3.5 



Per cent 
6 
5.5 

57 
30 
1.5 



It is to be noted, however, that wood pulp was used to some 

extent in i88o, but was not recorded and tabulated as a separate 

item. 

3. DEFINITION AND TYPES OF PAPER 

Paper is a matted or felted structure of fibrous material, formed 
into a relatively thin sheet. It is composed essentially of cellulose 
fibers obtained from vegetable growths in a more or less pure state. 
These fibers may be grouped as follows: (a) Seed fibers, or seed 
hairs, (&) stem or bast fibers, (c) leaf fibers, (d) fruit fibers, and (e) 
wood fibers. In general, it is customary to consider and classify 
paper according to its use rather than according to its constituents. 
In the testing of paper the use to which it is to be put determines 
the kinds of tests necessary to evaluate its quality. 

The classification of the various types of paper has not reached a 
satisfactory state, and the nomenclatvire and trade names are 
often very confusing to the layman. This is largely due to the 
lack of standardization, the difficulty of defining numerically 
certain qualities, and the fact that the distinctive line between 
various kinds of paper is, in many cases, so slight that it is almost 
impossible to tell by what name to call it. The following general 
classes of paper given in Table 2 refer to broad types, and in 
each class there are variations of constituents as well as quality: 

TABLE 2. — Percentage Output of the Several Classes of Paper Products 



Paper products 


Percentage 

of total, 

1918 


Fibrous materials used in varying proportions 




■30.4 

5.3 

.2 

15.3 

23.3 

2.0 

16.8 

5.8 

.9 


Old paper, wood pulp, straw, old rope 

Old paper, wood pulp, asbestos, waste, rages, etc. 

Rags, chemical wood pulp, cotton linters 

Rags, chemical wood pulp 

Mechanical and chemical wood pulp 

Chemical wood pulp, rags, old rope 

Old rope, rags, sulphite, and sulphate wood pulp 

Rags and chemical wood pulp 


Building 

Blotting 


News and hanging- 




Wrapping. . 




Specialties 







The Testing of Paper y 

II. QUALITY OF PAPER 

The production of paper was for many years an art, especially 

during that period before the paper machine came into general 

use. It is obvious, therefore, that in the past the quality of paper 

was judged and determined by empirical methods and esthetic 

standards which were in many cases crude from a scientific point 

of view. It is true that an experienced man may determine 

much in regard to a sheet of paper by tearing it, by examining 

the finish or siu-face, and by looking through the sheet toward 

the Kght. Yet in all such tests the individual must be very 

experienced, and there is always the personal factor to be 

considered. 

1. PtfRPOSE OF TESTS 

The use of scientific or technical tests on paper has little value 
unless the purpose for which the paper is to be used is taken into 
consideration. The tests described in this circular are those 
which have been found effective in determining the relative value 
of various grades of paper and are given in their present state of 
development. These tests do not always give sufficient data, 
but their accuracy is generally within the variation in uniformity 
of the paper. There are, however, certain qualities of paper 
that it is difficult to define or record numerically, such as " color," 
"finish," and "formation." These three quaHties are often the 
deciding factors in the purchase of paper, especially when it is 
not bought on specifications. It is therefore important to develop 
in the near future methods of testing these qualities. 

2. DEVELOPMENT OF TEST METHODS 

In the beginning of the development of paper-testing methods 
at this Bureau the methods used by foreign laboratories were more 
advanced and standardized than those in this country-, and many 
of the former were adopted. Since then various new methods 
and improvements have been developed in the United States, 
and one of the greatest contributory agencies was the growth of a 
technical association in the paper industry' It is true, however, 
that the requirements of the Government for various grades of 
paper and the need of placing these purchases upon a scientific 
basis have been a great stimulus at this Bureau in the develop- 
ment of the technique of paper testing. The large number of 
samples tested yearly to determine whether Government pur- 
chases have conformed to the specifications has given an opportu- 
nity for ascertaining the accuracy and suitability of the methods. 



8 Circular of the Bureau of Standards 

and has led to numerous changes and to the adoption of new 
methods. In general, it is necessary to develop tests for paper 
for a specific use. This is illustrated in the case of a tearing test, 
several of which have recently appeared in print; for in this case 
it was essential to find a test for wrapping paper which would 
reproduce service conditions more satisfactorily than with a 
bursting or "pop" test. In regard to certain other tests, such as 
the determination of the amount of rosin sizing in paper, it has 
been possible to simplify the procedure and to lessen the time 
required. The slight decrease in accuracy in the case mentioned, 
resulting from the use of the shorter method, limits its use to 
routine testing but conserves material and saves much time. It 
is becoming more and more apparent that no one testing device 
is applicable to all grades of paper, and it will be necessary to 
develop instruments for determining the physical qualities of 
each of the general classes of paper. This is illustrated by the 
fact that container board and tissue paper have difi'erent uses, 
are constructed differently, and should be tested differently. 
There is therefore a large field yet to be developed, not only in 
testing instruments but also in methods of analysis. Quality 
and uniformity depend in large measure upon methods of deter- 
mining quality and uniformity, and such methods and apparatus 
should be made more specific and refined. 

3. SPECIFICATIONS 

It is becoming increasingly common to purchase material ac- 
cording to an agreement between the purchaser and the con- 
tractor which is based on the value of the material for the purpose 
for which it is bought. In such cases it is customary for the pur- 
chaser or the contractor to submit specifications of the material 
in question, which specifications are agreed upon by both parties 
interested before the purchase is ratified. These specifications 
may be a vague understanding between the pm-chaser and the 
contractor, they may be a very indefinite statement of the merits 
of the material in question, but they are becoming more and 
more to be based on scientific and technical data. 

In the past, in the development of specifications for material, 
little attention has been paid to any particular standard for 
specifications, it being probably felt that each man or concern 
knew best how to write a specification. In many cases this led 
to a form detrimental to the purchaser, the contractor, or both. 
It is therefore thought that consideration should be given to 
specifications in general, which can then be specialized to meet 



The Testing of Paper 9 

the particular case. Witli this in view, a brief outline is herewith 
given on the methods of preparing paper specifications. This 
topic is not here treated as a comprehensive standardization of 
the method of preparation of specifications, but is given merely 
as a guide to the preparation of specifications in a field in which 
the uses of specifications are still in the process of development. 

(a) Formulation. — During the process of formulation of the 
specifications various interested contributory agencies should 
assist in revising them as first initiated. These specifications, as 
revised, should be finally agreed upon by the interested parties 
and be oflficially authorized. When so authorized they are given 
a certain oflficial status, whether it be between indi\'iduals, com- 
panies, associations, or industries. Care is to be taken that the 
scope of application or jurisdiction of the specifications be made 
clear, as well as their designated or implied lifetime. It is also 
very desirable to include standard practice for revision of the 
specifications and also a standard typography and format. 

(b) Nomenclature. — A standard terminology should be adopted 
and adhered to throughout the specifications. When possible 
references and authority should be given. Special conditions or 
limitations as to terminology should be included, and a means for 
a decision as to disputes on terminology may be of assistance. 

(c) Quality Standards. — As a preliminary to the specifications 
of the quality of the material to be purchased, it is desirable to 
name exactly and define the material in question. The use to 
which the material specified is to be applied should be considered 
in great detail. It is then necessary to have a qualitative descrip- 
tion of the useful properties desired and a statement of the unde- 
sirable properties. The quantitative statement of the useful 
properties, composition, dimensions, form, and structure, and of 
harmful or nonuseful properties, giving maxima and minima per- 
missible, is that part of specifications which is often considered most 
important. It is necessary, hov/ever, to include a qualitative 
and quantitative statement of tolerances permitted in each case. 

(d) Technical Practice. — A material piu-chased on specifica- 
tions must be tested in order to determine that it, on delivery, 
conforms to the specifications. Inspection and sampling are 
therefore necessary. Standard test methods must be a part of the 
specifications and naturally include a description of the test instru- 
ments and facilities to be used. Test certificates shotild be avail- 
able, the results properly interpreted, and the material accepted, re- 
jected, or subject to further test. All reports, records, and original 
data should be kept in available form. 

22848°— 21 2 



lo Circular of the Bureau of Standards 

III. PHYSICAL TESTING 

The physical quahties of paper, such as dimensions, weight, 
strength, and moisture content, are affected by atmospheric 
changes in temperature and relative humidity; but it is not pos- 
sible, with the limited information available, to determine the 
factors necessary to reduce the data obtained at one temperature 
and relative humidity to that which they would be at another 
temperature and relative humidity, or at a standard atmospheric 
condition. The variation caused by changes of temperature 
and relative humidity is not constant for paper, in general, and is 
seldom constant within a restricted class of paper. In order to 
obtain standard conditions in which to test the physical proper- 
ties of paper at this bureau, a large room has been equipped with 
an apparatus (Fig. i) which maintains a temperature of 70° F 
and a relative humidity of 65 per cent. These conditions have 
been decided upon rather arbitrarily, yet seem advisable for the 
following reasons: It is relatively easy to produce the conditions; 
it is an atmosphere in which it is not uncomfortable to work; these 
conditions are apparently approximately midway in the increasing 
and decreasing curves of strength, due to variation of temperature 
and relative humidity, as indicated by work already done; and, 
lastly, most of the laboratories which control testing conditions 
have adopted 70° F temperature and 65 per cent relative humidity 
as their standard and have collected their test data under those 
conditions. Therefore, all samples of paper tested for physical 
qualities that are affected by atmospheric changes are conditioned 
for at least 2 hours in this room before being tested. They are 
placed on a rack properly fanned out in order that as much of 
the paper may be exposed as possible. (Fig. 2.) 

1. WEIGHT 

For convenience in laboratory work, a ream 25 by 40 inches in 
size containing 500 sheets (25X40 — 500) has been adopted 
as standard. The data are obtained in pounds per standard 
ream and are then converted to the ream size required for the 
particular sample of paper in question. Ten sheets of paper, 
each ID by 10 inches in size, are weighed on a quadrant scale, 
illustrated in Fig. 3, having an average accuracy of approximately 
0.2 per cent between 20 and no and a maximum error of 0.5 per 
cent between the same points on the scale. There are several 
types of scales or weighing devices on the market which may be 



The Testing of Paper 



II 




Fig. I. — Apparatus J or maintaDung standard atmospheric conditions: Temperature, 

/■o° F, and relative humidity, 6^ per cent 

This apparatus automatically washes the return air, saturates it at a given temperature, and then raises 

the temperature cf air to a proper point so that standard conditions are maintained in the room 




Fig. 2. — Rack for conditioning paptr 

Samples of paper, before being tested, are subjected to the standard conditions, so that all papersmay be 

tested under the same conditions 



12 



Circular of the Bureau of Standards 




Fig. 3. — Scale for iveighing paper 
This type of balance is used for laboratory work in detennining the ream weight of paper 




Fig. 4.- — Thickness tester 
The thickness of the paper is read off on a dial in thousandths of an inch 



The Testing of Paper 



13 



used for this purpose. It is obvious that the samples being 
weighed must be accurately measirred to determine their size, and 
this is done by means of an accurate rule, graduated in tenths of 
inches. The following formula is of assistance, where a is scale 
reading, b is one dimension of the sample, c is the dimension at 
right angles to b, and d is the number of sheets of paper in the 
sample : 

a X 1000 ... 

J— — — -1 = weight m pounds per ream 25X40 — 500. 

^ C /\ CI 

For samples of paper weighing less than 20 on the quadrant scale 
a chemical balance is used. For convenience, the following 
formula is used : 



= Weight in 



(Weight in grams) X (1.102) X (1000) 

(Area of sample in square inches) X (number of sheets) 

pounds per ream 25X40 — 500. To convert the weight of the 
standard ream to the weight of a ream of the desired trade size, 
it is only necessary to multiply the weight of the former by the 
area of the latter and divide by 1000, provided, of course, that 
the latter ream contains 500 sheets. This is illustrated in Table 3. 

TABLE 3.— Typical Equivalent Weights in Standard and Trade Sizes 



Weight of ream, 
25 X 40—500 


Trade size ream, 
500 sheets 


Area of sheet 


Weight of 

ream, trade 

size 


Pounds 

52.6 

64.2 
100.0 
156.0 


Inches 
25 X 38 
17X22 
20X25 
22.5X28.5 


Inches - 
950.0 
374.0 
500.0 
641.3 


Pounds 
50 
24 
50 
100 



This scale may be calibrated by placing small accurate weights in 
the pan and taking readings on the scale. An average of several 
readings at uniform distances apart on the scale should be obtained. 

2. THICKNESS 

There are a number of instruments or devices available for de- 
termining the thickness of paper. They are, usually, a spring 
micrometer with the dial graduated into thousandths of an inch, 
as shown in Fig. 4. It is not advisable to take readings much 
closer than half of one-thousandth (0.0005) of ^.n inch. Some diffi- 
culty is experienced at times with the spring of the micrometer, and 
the needle or pointer should be adjusted to zero whenever it does not 



14 Circular of the Bureau of Standards 

properly return there. The thickness tester is caHbrated by means 
of standard sheet metal leaf gages. Since the spring is not com- 
pressed to any great extent when testing most grades of paper, the 
error introduced by varying pressure exerted bj' the spring against 
the paper is not great. Thickness test is made on each of the lo 
sheets of paper of which the test sample is composed, and an 
average is obtained which is reported as thousandths of an inch. 

3. BURSTING STRENGTH 

The biu-sting strength is the apparent pressure necessary to 
burst a hole in a sheet of paper, when the pressure is exerted against 
a definite area and the sheet is held taut by a clamp. There are 
several types of such instruments available, but there seems to be 
no definite relation between the data obtained with them. In any 
case, such an instrument is empirical and the data obtained ■w"ith 
any one machine are relative. Various factors in the paper influ- 
ence the test, such as kind and length of fiber, type or formation, 
weight, thickness, etc. One of the most important factors is the 
stretch or elongation of the paper under presstue or strain. 

The type of instrument used at this time at this Bureau for this 
test is one in which a handwheel, actuating a piston, forces glycerin 
(glycerol) against a flexible diaphragm which transmits the pressure 
to the sheet of paper. The paper is held in place by an annular 
ring and the hydrostatic presstue within the chamber is indicated 
on a suitable gage, as illustrated in Fig. 5. A test is made on each 
of the 10 sheets of the test sample and an average of the gage read- 
ings is obtained. It is of considerable value in comparing the 
bursting strength of various samples of the same class, but of differ- 
ent weight, to reduce the biu-sting strength to a unit weight basis. 
This is done by dividing the bursting strength by the weight of the 
standard size ream (25X40 — 500), and the result or ratio when 
multiplied by 100 is reported for convenience as a percentage. 

It is obvious from a study of such a device that there are 
several factors in its design and construction that may influence 
the value of the test and the data obtained. These are as fol- 
lows: The age and condition of diaphragm, the pressiure of the 
clamp (except in the case of the lever clamp type), the amount 
of glycerin in the cylinder, the speed and uniformity of rotation 
of the handwheel, and the accm-acy of the gage. The flexible 
diaphragm deteriorates, whether used or not, when exposed to 
air and in contact with the glycerin, and is renewed every month. 
In this connection it is to be noted that the area of the diaphragm 
in contact with the paper at various presstues is not constant. 



The Testing of Paper 15 

For this reason all results are recorded and reported as "points" 
(gage-scale divisions), rather than as pounds per square inch. 
Precaution should be taken to be sure that the cylinder is full of 
glycerin — that is, that there is no air present within the chamber, 
since otherwise the results are not reliable. It is important 
that the handwheel be turned at a uniform rate, and 120 rpm has 
been adopted as standard. The pressure gage is calibrated 
every month by means of a dead-weight tester, and corrections 
applied when necessar\^ 




I'lG. 5. — Bursting strength tester 

The sample of paper is burst by means of pressure exerted tlirougfi a rubber diaphragm whidi conforms 

to the shape of the paper 

4. TENSILE STRENGTH 

There do not seem to be any instruments of American manu- 
facture built for the purpose of determining the tensile strength 
of paper. The apparatus illustrated in Fig. 6 is of foreign manu- 
facture and is used, with some modifications, for testing both 
paper and textiles. A strip of paper 15 mm wide is clamped 
in the jaws, so that the distance between them is 90 mm. By 
means of a piston, hydraulically operated, the lower jaw is pulled 
away from the upper one, and the lever arm with the weight on 
the end is brought out at an angle until rupture of the paper 
takes place. A ratchet with pawls holds the arm at the point 
on the scale where the break occurred. This scale is graduated 
in fractions of kilograms and has a capacity of 50 kg. A second- 
ary scale, midway up on the lever arm, gives the elongation of 
the strip of paper at the point of rupture. 



i6 



Circular of the Bureau, of Standards 




Fig. 6. — Tensile testing inachiiie 

By means of tliis instrument the tensile strength of paper and the elongation at rupture may be deter- 
mined 



The Testing of Paper 17 

In making the tensile test on paper, 10 test strips, each 15 mm 
wide and 150 mm long, are carefully cut from the test sample in 
both the "machine" and "cross" direction. An average of the 
results is obtained and is generally converted into pounds per 
inch of width of sample by multiplying by the factor 3.732. A 
useful strength factor is obtained by reducing the tensile strength 
to the "breaking length," or the length of paper which, if sus- 
pended by one end, would break of its own weight. This factor 
is obtained by the following formula: 

Tensile strength in pounds per inch 

widthxi3 889 td , • 1 *, • , 

„r • 1 .^- 3 — i 7 — r, ^ = Kreakmg length ni yards. 

Weightmpoundsof ream (25X40-500) » » j 

There are several factors of importance to be considered when 
operating this apparatus. The sample should be properly ad- 
justed in the jaws, so that there is no uneven diagonal strain on 
the strip or incorrect aUgnment. This is sometimes difficult, 
as the upper jaw is not rigid. The test strip should be accurateh' 
cut along the ' ' machine ' ' direction of the test sample or at right 
angles to that, never diagonally across. The regulating valve of 
the water supply should be adjusted to permit a downward speed 
of 3 inches per minute of the lower jaw. It is obvious, however, 
that if two papers are tested at the same rate and one sample has 
twice the percentage stretch of the other, that the time to break will 
differ for the two papers. The apparatus is caUbrated once a year 
by hanging acciu^ate weights by a thread or light string from the 
upper jaw and determining the points on the scale which should 
correspond. The difference is the necessary correction. 

5. FOLDING ENDURANCE 

The folding endurance of a sample of paper is obtained by a 
machine which registers the number of alternate folds the sample 
will endure before breaking, while under a constant tension of i 
kg. The test strip, 15 mm wide and 90 mm long, is placed in the 
jaws and the apparatus is started. The strip is then folded flat 
upon itself, then opened and folded at the same Hue upon itself 
in the reverse direction, this being called a double fold. The 
number of double folds the sample will withstand before breaking 
is indicated on a dial and is reported as the folding endiarance. 
Five tests are made in both the "machine " and " cross " direction 
of the test sample, and an average is obtained. A speed of 120 
double folds per minute is maintained by means of a small electric 
22848°— 21 3 



1 8 Circular of the Bureau of Standards 

motor. This tester is illustrated in Fig. 7. It is to be noted, 
however, that the folding endurance test under tension seems to 
be more affected by atmospheric changes of temperature and 
relative humidity than most of the physical tests. The stretch 
of the paper is also a factor influencing the test. The calibration 
and standardization of the folding tester require much attention, 
since there are several moving parts that become worn. To 
obtain check results on different machines, it is necessary to check 




Fig. 7. — Folding tester 

The ioldinjj endurance of paper under tension is determined by the folding of a strip of paper, and the 

number of double folds which the samples will resist is indicated on the dial 

carefully the bearings, rollers, and the tension of the springs, and 
to have their dimensions all accurately the same. 

6. TEARING STRENGTH 

A method of determining the tearing strength of paper has 
become of considerable importance, and a number of devices have 
been proposed for this purpose. The following method has been 
adopted tentatively until the conclusion of further work. For 
this test the tensile testing machine as shown in Fig. 8 has been 
adapted, with the weight taken from the lever arm. Ten strips 



The Testing of Paper 



19 




Fig. 8. — Tearing tester 
This is an adapted tensile testing machine with the weights removed to give it more sensitiveness; it 
is used for tearing a strip of paper in determining its resistance to tear. There are other devices being 
developed for this purpose 



20 Circular of the Bureau of Standards 

I inch wide are slit halfway down the middle and each half-inch 
end is placed in one of the jaws, the lower jaw being offset one- 
half inch as illustrated. A lineal downward speed of 3 inches per 
minute of the lower jaw is used, and the tearing strength is indi- 
cated as points on the scale. The apparatus must be calibrated 
with the weight off the lever arm, and a conversion curve may be 
plotted in order that the readings from the scale may be readily 
obtained in grams. 

Ten tests are made in both the "machine" and "cross" direc- 
tions, 10 sheets being used in each test to obtain an average. A 
maximum tearing strength in grams is obtained by this method, 
and the average of the 10 tests is reported as such. It is to be 
noted that with heavy or thick samples it is necessary to use a 
smaller number of sheets in each test sample, as there is a tend- 
ency for the tearing edges to rub or bind. This friction has been 
eliminated to a considerable extent by having the lower jaw offset, 
so that the tearing strain is parallel to the test strip. This test 
will probably be modified to some extent in the near future, as a 
maximum value is not always in agreement with service tests. 

7. ABSORPTION 

I'here are several methods for determining the absorbency of 
bibulous papers, and a study of these methods is now in progress 
to determine their relations. In the case of blotting papers the 
test should reproduce service conditions as much as possible, 
since not only the total absorption and the rate are important, 
but also the effect of repeated applications. In addition, the 
effect of ink in place of water during the test is to be considered. 
The method as given is used for testing the absorption of blotting 
paper, but is open to the criticism that the area of the cross section 
or thickness is not taken into consideration. 

In making this test, using the "strip" method, a strip of blot- 
ting paper 15 mm (about three-fifths inch) wide and 150 mm 
(about 6 inches) long is suspended, as illustrated in Fig. 9, so that 
the lower end dips 3 mm (about one-eighth inch) into a pan of 
distilled water. Beside the strip is a scale reading in millimeters 
(fractions of inches), and at the end of each minute for 10 min- 
utes readings are taken of the height to which the liquid rises in 
the strip. Five tests are made in both the "machine" and 
" cross " direction and an average obtained. The result is reported 
as the height to which the liquid will rise in 10 minutes. When 
necessary, or advisable, the same strips may be subjected repeat- 
edly to the test, which will indicate the decreasing ability to ab- 



The Testing of Paper 21 

sorb water or ink. In addition, a standard ink of the following 
formula may be used: 

Grams 

Tannic acid 23. 4 

Gallic acid ^ - 

Ferrous sulphate 30. o 

Dilute hydrochloric acid (II. S. P.) 25. o 

Phenol i_ o 

Bavarian blue, S. & J- No. 478 or similar suitable dye 2. 2 

Water to make a volume of looocc at 15.6° C. 




Fig. g. — Absorption tester 

This is one method of testing blotting paper, and the height of rise of hquid is indicated on the two sam- 
pies of paper, one on either side of the metric rule 

The method as given above is adopted tentatively and will be 
modified or changed if future work makes it advisable. Other 
methods have been suggested and are being investigated, such as 
the method when water or ink is allowed to drop from a i cc 
pipette, or a sample is totally immersed in water or ink for a 
given time and the percentage amount absorbed determined. 



22 



Circular of the Buremi of Standards 
8. TRANSPARENCY 



It sometimes becomes advantageous, in order to more specific- 
ally evaluate the efficiency of two or more samples of envelope 
windows, tracing paper or cloth, glassine paper, etc., to assign a 
numerical value to the opacity or transparency of the various 
samples. This is particularly advantageous if the quality of two 




Fig. io. — Transparency apparatus 
This is used for determining the relative transparency and opaqueness of papers 

similar papers is so nearly alike in this respect as to be indistin- 
guishable by ordinary observation. 

The Bureau has developed and adopted a standard method for 
determining the transparency of paper and tracing cloth, which 
is described in detail in B. S. Circular No. 63 and illustrated in 
Fig. 10. Briefly this method consists in placing a sample of the 
paper or cloth to be tested over two adjacent surfaces, one white 
and the other black, and meastaring the reduction in contrast of 
the appearance of the two surfaces. If the material in question 



The Testing of Paper 23 

is quite transparent, the contrast between the black and white 
starfaces as seen through the material will be quite noticeable; 
but if the material is opaque, none of the light incident upon its 
surface will be transmitted and absorbed by the black surface 
beneath and consequently there will be no contrast between the 
parts of the material covering the black and white sm"faces. 

In making the measurements one must use a photometer having 
a divided photometric field, one-half of which is illuminated by 
the light coming from the material over the white surface, while 
the other half is illuminated by the light coming from the mate- 
rial over the black surface. The two halves of the photometric 
field are then "matched" by visual observation and properly 
setting the photometer, and the indicated results are recorded. 
A simple computation based on these observations gives the nu- 
merical measurement sought, which is called the "contrast 
ratio." This varies between zero and unity, larger values indi- 
cating less transparency. 

IV. CHEMICAL TESTING 

The testing of paper to determine those constituents, other than 
fibrous materials, which may be harmful in excessive amounts is 
desirable, and for routine testing this is relatively simple. These 
constituents usually consist of sizing material, such as rosin, 
glue, or starch, and loading materials or fillers, such as clay, talc, 
and various other inert substances. There are other materials 
present in certain special papers which are not considered here. 

1. LOADING MATERIAL 

The determination of the amount of asli of the paper indicates 
the absence or presence of loading material, which is usually 
added for the purpose of giving the paper a smooth printing sur- 
face. Paper having an ash of less than 1.5 per cent usually has 
not had a filler added. In the case of all-rag papers the ash may 
be as low as 0.5 per cent, while with papers made from wood pulp 
it may be as low as 0.75 per cent. An ash greater than 1.5 per 
cent usually indicates that some loading or coating material has 
been added, except where old papers were used, or a pigment dye 
for coloring. The percentage of ash obtained includes nonvolatile 
and noncombustible materials from several sources, as follows: 
(a) Ash due to residual minerals in fibrous pulps, (6) ash due to 
loading material, (c) ash due to surface coating, and (d) ash due 
to mineral coloring materials or pigments and a slight residue 
from sizing. 



24 



Circular of the Bureau of Standards 



A I -gram sample of the paper, obtained by taking equal portions 
from each of the lo sheets of the test sample, is weighed and placed 
in a nickel crucible. This is placed in an inclined position upon a 
triangle over a Bunsen burner, as illustrated in Fig. 1 1 . The 
paper first scorches, then carbonizes and finally ignites. When the 
paper begins to bmn, the crucible is removed from the flame and 
the paper is allowed to burn quietly. During the burning care 
must be taken that none of the ash is lost by air currents. To 
prevent this a cover may be placed partially over the crucible. 
After the burning is complete the crucible is then replaced on the 




Fig. II. — Means of determining Ihe loading in paper 

This illustrates a convenient way of determining the ash in paper when there are many samples daily, 
and shows the various positions of crucibles during the operation 

triangle and the heat applied vmtil the last traces of carbon have 
disappeared. In some cases it is necessary to use a blast lamp to 
consume the last traces of carbon. After the crucible has cooled 
the ash is transferred to a counterpoised aluminum pan and 
weighed. The result is obtained directly as a percentage. For 
extremely acctuate work the moisture in the paper should be elimi- 
nated by drying at loo to 105° C before weighing out the sample 
for test, and the ash in the crucible should be cooled in a desiccator, 
as a variation of 2 per cent in moisture content mil give an error 
of 0.02 per cent for each per cent of ash. 



The Testing of Paper 25 

To determine the kind of loading or coating material used, it is 
necessary to test the ash qualitatively, for which purpose at least 
o.2g. of ash is desirable. Briefly, tests should be made for the 
substances indicated in Table 4, in which are also given the fillers 
that the presence of these substances would indicate. 

TABLE 4.— Paper FUlers and Their Indicators 



Substance sought 



Filler indicated 



Calcium sulphate 

Calcium carbonate 

Barium sulphate 

Magnesium silicates. . 
Aluminum silicates. . . 



Crown filler 
Chalk 
Blanc fixe 
Talc 
China clay 



These fillers have various trade names and do not in all cases 
have definite chemical formulas, but the presence of any great 
amount of any of the materials in the first column would indicate 
the kind of filler used, and further confirmatorv tests mav be 

made. 

2. SIZING 

Nearly all grades of paper, except blotting, filter, and similar 
papers, have a sizing material added to give certain properties to 
the paper, including ink resistance. The sizing material is added 
during the preparation of the stock for the paper machine and, 
in some cases, is added after the paper is made by passing the 
sheet through a bath or tub containing glue, treated starches, or 
other similar material. In the first case rosin is used, and the 
paper is said to be "engine-sized"; in the latter case the paper is 
"tub-sized." It is desirable to determine the presence and 
amount of these sizing materials, and this is done bv chemical 
analysis. It is not necessarily true that the percentage of sizing 
material will indicate the resistance of the paper to ink; for this 
purpose other methods are being developed. 

(fl) Total Resins. — The following methods are used for de- 
termining total resins: Five grams of paper are cut in strips 
aboutone-half inch wide from the 10 sheets of the test sample and 
are folded into numerous small crosswise folds. These are placed 
in the siphon cups and acidulated alcohol (900 cc of 95 per cent 
alcohol, 95 cc distilled water, and 5 cc glacial acetic acid) is poured 
into the cup until it starts to siphon over, \\nien this has entirely 
siphoned over into the shell-shaped extraction flasks, approxi- 
mately 20 cc more of the acidulated alcohol is added to the siphon 



26 



Circular of the Bureau of Standards 



cup, which is then hung on the condenser, as illustrated in Fig. 12. 
The flask is set into the steam bath and the extraction proceeds 
for about 2 hours, or until the cup has filled and siphoned over 
about ten times. The extract is poured into a weighed glass dish 
and the flask washed out with a small portion of the acidulated 
alcohol, which is added to the original extract. The alcohol is 
then evaporated, the dish dried and vceighed, and the increase in 
weight of the dish divided by 5 will give the percentage of total 
resins. 




Fig. 12. — Rosin sizing extractor 
This illustrates a convenient form of apparatus for determining the amount of rosin sizing in paper and 
shows the type of extraction thimbles and condensers. The chief criticism of this is that it is difficult to 
save the solvent, and where expensive solvents are used this form is not practical 

For additional accm-acy other than for routine testing or con- 
trol work, the following additional method is advisable: 

Just before the extracted total resins in the glass evaporating 
dish, in the method given above, go to dryness, they are cooled 
and taken up with 25 cc of ether, and transferred to a 250 cc 
separatory funnel containing 100 cc of distilled water and 25 cc of 
a satixrated solution of sodium chloride, the latter being present 
to prevent the formation of an emulsion. The funnel is shaken 
thoroughly and the contents allowed to separate. The water is 
drawn off into a second separatory funnel, and this is washed 



The Testing of Paper 27 

again with 25 cc of ether. The two ether extracts are combined 
and washed two or three times with 100 cc of distilled water to 
remove all the salt and foreign matter other than ether-soluble 
resins. Should glue which is extracted from the paper by the 
alcohol interfere by emulsifying with the ether, it may readily be 
removed by adding a strong solution of sodium chloride to the 
combined ether extracts, shaking thoroughly and draining it off, 
repeating if necessary before washing with distilled water. The 
washed extract is transferred to a weighed glass dish, evaporated 
to dryness slowly, dried in an oven at 95 to 100° C for one-half 
hour, cooled, and weighed. The increase in weight of the dish 
divided by 5 will give the percentage of total resins. 

A quaHtative test for rosin may be made by the following 
method: A small portion of the paper boiled with 5 cc of acetic 
anhydride in a test tube, cooled, and treated with a few drops of 
concentrated sulphuric acid added so as to slip smoothly down the 
side of the test tube, will develop a pink ring if rosin is present. 
The cover of a porcelain crucible may also be used, and in this 
case a drop or two of each of the liquids are brought together by 
glass rods. A pink color may develop where the two come together. 

(b) Starch. — Starch is present to some extent in some papers, 
and this may be indicated by placing a few drops of a pale yellow 
dilute solution of iodine in potassium iodide on the sample of 
paper. The development of a blue color indicates the presence 
of starch. If it is possible to extract a sufficient amount of the 
starch from the paper by warming with water, a few drops of the 
solvent containing the starch is placed on a slide, dried, and 
examined under the microscope. In this way the kind of starch 
used may be determined by the shape and markings of the 
granules, provided the starch was not sufficiently cooked to de- 
stroy the grains. For the quantitative test for starch, the starch 
may be converted into dextrose by treating a few grams of paper 
in water with dilute sulphtuic acid and estimating the amount of 
dextrose present in the extract by Fehling's solution. 

(c) Glue. — The presence of glue in paper may be indicated by 
either of the following methods: (i) The extract obtained by 
boiling I g of paper in water is decanted into a test tube, cooled, 
and treated with a few cc of ammonium molybdate solution, 
followed by a few drops of nitric acid. The presence of glue is 
indicated by a white amorphous precipitate. (2) The extract ob- 
tained by boiling i g of paper in water is decanted into a test 
tube, cooled, and treated with a iew cc of tannic acid solution of 



28 Circular of the Bureau of Standards 

5 per cent concentration. The presence of glue is indicated by a 
heavy flocculent precipitate, which, when heated, becomes co- 
agulated and hard. 

Glue may he determined quantitatively by treating 3 to 5 
grams of paper by the Kjeldahl method and thus determining the 
amount of nitrogen present. The percentage of nitrogen obtained 
multiplied by 5.6 will give the percentage of glue in the sample of 
paper. This test, however, is of no value when both glue and 
casein are present, since both contain nitrogen. 

V. MICROSCOPICAL TESTING 

In the examination of paper to determine its quality, it is neces- 
sary to have a means of identifying the fibrous materials from which 
the paper is made, since some fibers do not deteriorate as rapidly as 
others. These materials are chiefly as follows: Rags; chemical 
wood pulp, consisting of coniferous and deciduous or broad -leaf 
woods; mechanical or ground-wood pulp; manila and jute; and 
straw. These occur in some ^ cases separately but more often in 
combination. In addition to identifjdng the presence of these 
various fibrous materials, it is necessary to determine the amount 
of each present in the paper. Since, however, the determination 
of rag in a paper, for instance, does not indicate the grade of rag 
used in the manufacture of the paper, specifications built up 
primarily about the fiber content of the paper are not always the 

best. 

1. PROCEDURE 

It is important to obtain a representative sample, and for that 
reason a small comer, about as large as a penny, of each of the 10 
sheets of the test sample is cut off and torn into small pieces. 
These are placed in a 50 cc beaker and approximately 20 cc of a 
0.5 per cent solution of caustic soda is added. The beaker is placed 
on a hot plate or stove and brought to a boil, but the boiling is 
not continued for more than a minute or two. The liquor is 
drained off and the pieces of paper are washed several times with 
tap water, care being taken that none are lost. They are then 
washed with approximately 20 cc of 0.5 per cent solution of hydro- 
chloric acid, and then washed twice more with tap water. A 
portion of the small pieces is rolled between the fingers into a pill 
about the size of a small pea and transferred to a test tube, which 
is half filled with water. The test tube is placed in a shaking 
machine, as illustrated in Fig. 13, and shaken until the paper is 
disintegrated into fibers, which normally takes about one-half 
minute. By means of a glass tube of about 5 mm internal diameter 



The Testing of Paper 



29 




Fig. 13. — Test tube shaker 

This device quickh' disintegrates the samples of paper into fibers and eliminates all the necessity of 

doing it laboriously by hand 



30 Circular of the Bureau of Standards 

a representative amount of the fibers is transferred to a glass slide 
and the water removed by placing several thicknesses of hard 
filter paper on either side of the slide. After the excess water has 
been thus removed, a strip of filter paper is placed on the fibers to 
absorb any traces, leaving the fibers dry but not so dry that there 
will be difficulty in separating them. Two or three drops of the 
zinc-chloride-iodine stain described below are placed on the fibers, 
which are teased out with steel needles until the fibers are reason- 
ably uniformly distributed and free from knots of fibers. 

Composition and Preparation of Zinc-Chloride-Iodine Stain ^ 

25 cc saturated zinc chloride solution at 70° F 
5.25 g potassium iodine 
0.25 g iodine 
12.5 g distilled water 
The three last ingredients are mixed together and the zinc chloride 
added. The insoluble matter is allowed to settle at least overnight and 
the supernatant liqtiid is decanted off. The stain must be kept in the 
dark or in a bottle opaque to light. It may be made up in larger quanti- 
ties, provided it is kept from the light and air. 

After the fibers are properly teased out with the needles, another 
but thinner glass slide is placed on top of the first slide, and the 
excess stain is squeezed out and absorbed by blotting paper. The 
slide is now ready for the microscope, which is of the binocular type, 
using artificial illumination as indicated in Fig. 14, and having a 
magnification of about 50 diameters. Care must be observed to 
keep the slide away from the light before using it for the estimation, 
and in any case the estimation should be made at least within 
one hom- from the time the slide was made up. Under the 
microscope, using the zinc-chloride-iodine stain, the fibers appear 
colored, as follows: 

Cotton and linen rags 



. Cooked and bleached manila J^^"^ ^^^ 

Cooked and bleached wood pulp ] 

Cooked and bleached straw and esparto f^^^^ ^° ''^"'^ ^'"'^^ 
Mechanical or ground wood pulp. . 1 

Jute, uncooked, and manila Wellow to lemon yellow 

Highly lignified fibers J 

In making the estimation both the distinctive shape and mark- 
ings of the fibers, as well as the colors as developed by the zinc- 
chloride-iodine stain, are of importance. Extreme care must be 
observed to have all beakers, test tubes, needles, and even fingers 
free from any fibrous material before beginning the preparation of 
a sample or slide. 

2 This formula is tentati^ e. Its value is subject to a number of factors that are now being studied. 
Additional information may be obtained from the paper section, Bureau of Standards. 



The Testing of Paper 



2. ESTIMATION 



31 



For general work and rovitine testing, the estimation method 
has been adopted. This consists primarily of properly judging or 
estimating the relative proportions of fibers present, after studying 
various fields of the slide. For this purpose standard samples of 
knov/n content are essential, and there are available here most of 
the more common commercial mixtures of fibrous materials, made 
up under rigid conditions. Since the accuracy of this method 
depends largely nn the experience of the operator, and since there 




Fig. 14. — Binocular microscope and daylight lamp 

For estimating and examining fibers it is desirable to have constant light conditions, and the use of a 

binocular microscope is of assistance when there is much continuous estimating work 

is a tendency to judge or estimate by appearance or area, it is 
most necessary, even for the experienced operator, to refer in many 
cases to the standard samples. This is especially true in the case 
of ground wood, since the specific gravity of this material is not 
the same as that of rag pulp or chemical wood pulp, and if standard 
samples are not used low estimations are obtained. It is to be 
noted that the percentage of various fibrous materials present is 
given on the basis of the total fiber content alone and nonfibrous 



32 Circular of the Bureau of Standards 

materials are not considered. There are other methods besides 
the one given for determining the amounts of various fibrous 
materials in paper, but most of these are not suihciently rapid for 
routine testing, and it is a question whether their accuracy is 
much greater. 

3. MICROPHOTOGRAPHY 

It is often necessary to have a permanent record of the fiber 
content of paper and also to have an opportunity of studying the 
characteristics of the various fibers. For this purpose a com- 
plete photomicrographical equipment is available, and Figs. 15, 
16, 17, and 18 illustrate the distinctive markings of various fibers. 
This field of research has not yet been sufficiently developed, but 
it opens considerable opportunity. The methods employed are 
those commonly used with such equipment, except that a 20-foot 
bellows permits of a flatter field on the photographic plate and 
greater definition. The use of monochromatic light is also of 
great assistance. 

VI. BIBLIOGRAPHY 

Most of the data and information on paper testing have been 
published as articles in magazines and periodicals. The books 
referred to are those most available at the present time. The 
periodicals given are those of greatest circulation with the technical 
men of the industry, but there are others containing at intervals 
articles on paper testing. The results of investigations of Gov- 
ernment laboratories have generally been published in the trade 
periodicals. Reference is also made to the secretary of the Tech- 
nical Association of the Pulp and Paper Industry at 542 Fifth 
Avenue, New York City, N. Y. 

1. BOOKS 

Sindall, R. W., Paper technology', 253 pp., 13 plates, 1158 illustrations; 1906. Lon- 
don, Charles Griffin & Co. An elementary manual on the manufacture, physical 
qualities, and chemical constituents of paper and of paper-making fibers. 

Cross, C. F., and E. J. Bevan, A text-book of papermaking, 507 PP-. 16 plates, 99 
illustrations, 9 pp. bibliography; 1916. London, E. and F. N. Spon (Ltd.). Contains 
a chapter on paper testing. 

Herzberg, Wilhelm, Papierpriifung (Paper testing), 146 pp., 65 cuts, 16 plates; 1902. 
Berlin, Verlag von Julius Springer. An introduction to the study of paper. 

Klemm, Paul, Handbuch der Papierkunde (Handbook of paper technology) 00, 4 pp., 
130 cuts, 3 colored plates; 1910. Leipzig, Th. Grieben's Verlag. With references 
and instructions concerning the use, manufacture, testing, and selling of paper. 

2. PERIODICALS 

Paper, Paper (Inc.), 251 West Nineteenth St., New York City, N. Y. 
Paper Trade Journal, Lockwood Trade Journal Co., 10 East Thirty-ninth St., New 
York City, N. Y. 



The Testing of Paper 



33 




Fig. 15. — Micropihotograph of Douglas spruce fiber (Pseudafsuga 
taxifolia). X 100 




Fig. 16. — Micro photograph of sugar or hard maple fi In 
{Acersaccharum). X ^00 



34 



Circular of ike Bureau of Standards 




^M 


r 




Fig. 17. 


— Microphoiograph of fibers from rag pulp. 


X 100 


ll^ss^^^ 


im '^^ ^%fc "'. at-'^. 


"■'- 'H 




Fig. 18. — Micro photograph of spruce ground wood fiber (Picea 
canadensis). X 100 



The Testing of Paper 35 

The Paper Industry, E. B. Fritz, publisher, 356 Monadnock Block, Chicago, 111. 

Pulp and Paper Magazine of Canada, Industrial and Educational Publishing Co. 
(Ltd.), Garden City Press, St. Anne de Bellevue, P. Que., Canada. 

N. B. — For reference to special articles on paper testing appearing in these period- 
icals, the Committee on Paper Testing and the Committee on Bibliography, both of 
the Technical Association of the Pulp and Paper Industry, 542 Fifth Avenue, New 
York City, N. Y., and the Bureau of Standards. Washington. D. C, should be con- 
sulted . 

3. GOVERNMENT PUBLICATIONS 

The testing of materials, B. S. Circular No. 45, 89 pp.; 191 j. Washington, Govern- 
ment Printing Office. Contains description of tests made on paper, see pp. 59-62. 

Specifications and tests for transparency of paper and tracing cloth, B. S. Circular 
No. 63, 8 pp.; 1917. Washington, Government Printing Office. 

Sammit, C. Frank, A measurement of the translucency of paper, Department of 
Agriculture, Bureau of Chemistry Circular No. 96, 3 pp.; 1912. Washington, Govern- 
ment Printing Office. 

Sammit, C. Frank, The detection of faulty sizing in high-grade papers, Depart- 
ment of AgTiculttU"e , Bureau of Chemistry Circular No. 107, 3 pp.; 1913. Washing- 
ton, Government Printing Office. 

Surface, Henry E., Bibliography of pulp and paper industries. Department of 
Agriculture, Forest Service Bulletin No. 123, Forest Products Laboratory .Series, 48 
pp.; 1 91 3. Washington, Government Printing Office. 

VII. REGULATIONS REGARDING TESTS 

The Bureau is equipped to make complete examination of 
papers for Government offices or bureaus, and will, in its discre- 
tion, perform similar service for the general public, when asked 
to act as referee or where the nature of the case calls for an au- 
thoritative test. The Bureau thus reserves the right to accept 
or decline requests for tests, depending upon the conditions in each 
instance. 

In order that the user may more correctly judge a paper and 
determine its usefulness for the purpose intended, he should be 
informed upon the following points: 

(q) Weight per standard ream 

(b) Thickness 

(f) Bursting strength 

{d) Tensile strength 

(e) Folding endurance 

(/) Tearing strength 

ig) Absorption 

(h) Amount and kind of loading material 

(i) Amount and kind of sizing material 

( ;') Fiber composition 

1. FEES 

All tests for the National and State Governments are made free 
of charge. For municipal governments and private parties 
charges are made according to nature and extent of the work 



36 



Circular of the Bureau of Standards 



required. Where such tests are accepted the fees will, in general, 

be based upon the following schedule, which states the fee for 

each test on a single sample and the charge for the same test on 

each additional sample, where several are submitted at the 

same time. 

FEE SCHEDULE 212.^Paper Materials 



Test 



212a. 
212b. 
7.12c. 
212d. 

2126. 
212/. 
2I2<7. 
212 h. 
212?'. 
212 j. 



Weight determination 

Thickness determination 

Bursting strength test 

Tensile strength test 

Folding endurance test 

Tearing strength test 

Absorption test 

Ash content determination 

Total resin determination 

Fiber composition determination 



First 


Each 


sample 


additional 


$1. 00 


$0.75 


•SO 


■5° 


I. 00 


■75 


2. 00 


1-50 


2. CO 


1-50 


2. 00 


1-50 


2. 00 


1-50 


I. 00 


•5° 


2.50 


2. 00 


3.00 


2. 00 



All samples of paper should be put up for shipment carefully 
protected by cardboard or other material to insure arrival in good 
condition. All paper samples themselves should be plainly 
marked "For Paper Section, Bureau of Standards, Washington, 
D. C." 

A careful record should be kept by the sender, so that the identi- 
fication marks may be used in the certificate to avoid repeating 
the detailed description of the paper. Samples submitted by 
Government departments should be marked in upper left-hand 
comer of sheet as follows: 

Date — Identitication marks. 

Submitted by: 

Kind of paper, 

Item number, 

Name of manufacturer. 

Tests for compliance with schedule. 

Remarks: (Any other information concerning the paper). 

Samples submitted by private parties, mark in upper left-hand 
comer of sheet as follows : 

Date — • Identification marks. 

Submitted by: 

Kind of paper. 

Use of paper. 

Ream size and weight, 

Test required , 

Remarks: (Any other information concerning the paper). 



The Testing of Paper 37 

As soon as the fee is assigned to the test, a bill is sent at once, and 
payment should be in advance, made by money order or check 
drawn to the order of the "Bureau of Standards." Results of 
tests are not certified until fees are paid. 

2. SAMPLING 

The following should be noted in regard to submitting samples 
for test : 

Whenever possible, 10 sheets of each sample, accurately cut 12 
by 10 inches, should be submitted. These sheets should be picked 
out in such a manner as v/ill most nearly represent an average of 
the total amount in question. The 10 sheets of each sample should 
be carefully fastened together, and one outside sheet should be 
marked as indicated above. 

In order to secure representative samples for test, it is advisable 
to proceed as follows: 

Case lots. — Select one case from each one-third of the paper in 
question, and then select one sheet from each one-third of each 
case. The tenth sheet should be taken from a fourth case. After 
cutting to the proper size for forwarding for test, the remainder 
of the sample should be saved for record piuposes. Paper in 
" frames " and bundles should be sampled in the same way. In the 
case of small boxes or packages, when possible, a sheet should be 
obtained from each of 10 boxes. 

Rolls. — Sample by taking i sample from each of 10 rolls not less 
than 4 sheets in from the outside of the roll. 

Washington, September 18, 1920. 



